Asphalt shingles are made by a process in which asphalt is mixed with inorganic filler material to make a filled asphalt coating, and the filled asphalt coating thus produced is used to saturate and coat a glass fabric mat. In this process, it is desired that the viscosity of the asphalt/filler material be sufficiently low so as to allow efficient processing at relatively high production rates.
The viscosity of the filled asphalt coating used in this process can often be a limiting factor in achieving complete saturation of the glass fabric. Such viscosity is typically a function of, e.g., the type of asphalt used, the level of inorganic filler in the asphalt coating, the type of inorganic filler used, and the temperature of the filled asphalt coating.
As the viscosity of the filled asphalt coating increases above certain ranges, the glass fabric mat may not be fully saturated, and thin or uncoated spots, bubbles or voids may be created which may lead to premature failure of the roofing shingle.
When the viscosity of the filled asphalt coating increases to unacceptable levels, the roofing shingle manufacturer must compensate for this increased viscosity by, reducing the “process line speed” and/or increasing the temperature of the filled asphalt coating and/or reducing the amount of filler in the asphalt/filler composition.
The problem with decreasing the “process line speed” is that it results in decreased productivity.
The problem with increasing the temperature of the filled asphalt coating is described, e.g., in U.S. Pat. No. 4,634,622, the entire disclosure of which is hereby incorporated by reference into this specification. This patent discloses that “Because asphalt is more expensive than the conventional filler material, the use of less asphalt overall, without reducing the amount of filler, has been tried by others. The result has been a cheaper roofing product, but one which cannot weather to the same level as product with more of the same quality asphalt. Further, a significant reduction in asphalt can create processing problems. The more the amount of asphalt in a given mix is reduced, the higher the concentration of filler in the mix. This increases the viscosity of the mix and could cause flow problems through the processing conditions. One way to combat this is to heat the asphalt or the filler or both, since the addition of heat will lower the viscosity. The addition of heat over and above the standard processing temperatures, however, would move the temperature of the asphalt closer to its flashpoint.”
The problem with reducing the amount of filler in the asphalt/filler composition is that, as is indicated in such U.S. Pat. No. 4,634,622, “ . . . asphalt is more expensive than the conventional filler material . . . . ”
It is an object of this invention to provide a filled asphalt coating composition that can be used to efficiently produce good roofing shingles that are relatively inexpensive and have good mechanical and other properties.